If you are considering visiting the cinema this week and fancy something naughty, depraved and downright sleazy, then Filth should be right up your alley but be warned: it doesn’t hold any punches and as deeply shocking as it gets, it will surprise you that at its heart is a subject matter that is dealt with sensitivity. Oh, and it has a towering central performance too.

Bruce Robertson is a Scottish cop on the verge of a promotion that he desperately wants. Only thing is, Bruce is far from your average cop. He snorts coke, gets drunk and is a total sex addict. He also lies, cheats, steals just to get his own way. With the case of a dead Chinese man by a gang of thugs, this could be a way up for Bruce but he is haunted by memories he doesn’t want and a steely determination to be the hero, win the day and the position. There’s one snag…he is his own worst enemy and it could be his downfall.

Based on the best-selling novel by cult writer Irvine Welsh, this has many similarities to his previous hit book-turned-into-a-movie, Trainspotting. Full of the weird and vile, it bounces around like an excitable kangaroo, never really knowing what plot strand to follow yet all the while it keeps you hooked throughout.

This is a film that you could never say was boring. It goes for the jugular and hangs on for dear life.It is a film that goes out to shock and, like at the screening I went to, some people will walk out. Don’t let this put you off because it is far more than just another offensive and sick film, it has real heart and soul.

Jon S. Baird, whose last film, Cass, was a surprisingly accomplished piece, does a terrific job with the directing. A neat visual flair, he uses images and quick editing, along with unusual shots to push us deeper and deeper into Bruce’s deranged and dangerous world. A trip to Germany, he goes for a grainy, 16mm feel, while Bruce’s nightmarish dreams involving his psychiatrist, Dr Rossi, are played out with a weird atmosphere and stranger camera angles. While it’s not as visually stunning as Trainspotting, it is never routinely shot, pushing the boundaries of cinema an inch at a time.

The performances are all terrific. Jamie Bell, as the young protegé to Bruce, is nicely naive, while Jim Broadbent, in a cameo role as Rossi, is deliciously odd with his Australian accent. Eddie Marsden is always good value and here, with his thick rimmed glasses, is fun as the nervously rich accountant, Bladese, who Bruce takes under his wing.

The main attraction is James McAvoy. Playing out-of-character, his performance is a tour-de-force: an evil, manipulative slime ball who gets what he wants no matter what he does. In the same breath, this is a remarkable piece of casting. McAvoy is such a likeable actor that even at his darkest and most monstrous moments, you somehow can forgive him of anything. Then throw on top of that the deeper layers of his complex character, that of a man who is trying to cope with grief and with a broken heart as well as mental health issues. A deeply complex character, it’s an incredibly strong performance from an actor who seems to get better with every role.

What really shocks about this film is the way it copes with mental health. Underneath all the sexual acts and drug taking and general bad behaviour is an honest and truthful look at someone desperately failing to cope with the issues and this has to be applauded. Never spoken down to or patronised, unlike most films, this one keeps it bubbling under all the time and then when you think things are going to be all right, something else happens.

The film is full of shocks and twists and none more so than the final act, which delivers some of the best twists in years. Filth may not be everyone’s taste but those who do go and see it will be in for a visual treat as well as a very satisfactory movie experience. It also includes the best soundtrack this side of Tarantino. Any film that can make David Soul’s Silver Lady cool is fine by me. A terrific film that challenges, evokes and shocks, this is funny, exhilarating and exhausting. A film that needs, nah, demands to be seen. A cult classic in the making.